Dual mode crt screen

ABSTRACT

A dual phosphor screen is deposited on the inside surface of the faceplate of a CRT. A photo electroluminescent panel made up of a layer of photoconductive material and a layer of electroluminescent material is placed on the outside surface of the CRT. A voltage is applied across the panel so that when ultraviolet energy illuminates the photoconductive material, the voltage change across the panel causes the electroluminescent material to be visible.

United States Patent [191 Potter [451 July 22, 1975 DUAL MODE CRT SCREEN [75] Inventor; Roy F. Potter, San Diego, Calif.

[73] Assignee: The United States of America as represented by the Secretary of the Navy, Washington, DC.

221 Filed: May 28,1974

21 App1.No.:473,987

[52] U.S. Cl 313/463; 313/467 [51] Int. CL WHOIJ 29/18; H01J 31/20; 1101.] 31/12 [58] Field of Search 313/473, 467, 463

[56] References Cited UNITED STATES PATENTS 2,423,830 7/1947 Fonda 313/473 2,861,206 11/1958 Fiore et a1. 313/463 X 2,898,475 3/1959 Larach 313/467 X 3,247,389 4/1966 Kazan 313/463 X 3,344,300 9/1967 Lehrer et a1 313/467 3,780,371 12/1973 Rymes 313/473 3,826,944 7/1974 Cooper 313/473 Primary Examiner-Robert Segal Attorney, Agent, or Firm-R. S. Sciascia; G. J. Rubens; T. M. Phillips [57] ABSTRACT A dual phosphor screen is deposited on the inside surface of the faceplate of a CRT. A photo electroluminescent panel made up of a layer of photoconductive material and a layer of electroluminescent material is placed on the outside surface of the CRT. A voltage is applied across the panel so that when ultraviolet energy illuminates the photoconductive material, the voltage change across the panel causes the electrolu minescent material to be visible.

2 Claims, 2 Drawing Figures 4 .llllllllll m: Alll'l .llulln...

PATENTED L 2 2 I975 ELECTRON FIG.

FIG.2

DUAE MODE CRT SCREEN BACKGROUND OF THE INVENTION In display systems it is often desirable to be able to have long and short persistence on a cathode ray tube used as the display device. In the past, various means have been used to effect dual mode CRT operation. Such means have included color filters combined with dual phosphors having the desired persistence characteristics and spectral responses separated sufficiently in wavelength, and the penetration type using layers of phosphors having the desired characteristics or the onion-skin phosphor shown and described in US. Pat. No. 3,522,463. In the latter the depth of penetration of the cathode ray beam determines which phosphor is excited, thus the control is electronic. However, the higher beam voltages and current required have a deleterious effect upon the phosphor screen and result in shortened tube life. The external filters are undesirable because of mechanical requirements and spectral shortcomings.

SUMMARY OF THE INVENTION The present invention provides a dual mode screen for a cathode ray display tube permitting operation in a short persistence or normal television scan ratio mode and a long persistent mode as in radar displays. The mode switching is accomplished by means of photoelectronically changing the voltage on the luminescent screen.

OBJECTS OF THE INVENTION An object of the invention is the provision of a dual mode screen for a cathode ray display tube permitting operation in short and long persistence modes.

Another object of the invention is the provision of a dual mode screen for a cathode ray display tube permitting operation in short and long persistence modes which overcomes the disadvantages of prior known devices of this type by extending the tube life.

Another object is the provision of a system for electronic switching from long persistence mode to short persistence mode and vice versa of a cathode ray display tube without alteration of the cathode ray beam electronic controls.

A further object is the provision of a dual persistence control wherein the two phosphors can be easily separated in wavelength resulting in a minimum of interference.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the follow ing detailed description when considered in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a cross-sectional view of a cathode ray tube showing the structure embodying the invention.

FIG. 2 is a schematic diagram showing the electrical circuit associated with the structure of claim 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings wherein there is shown that portion of a cathode ray display tube necessary to illustrate the invention. A dual phosphor screen composed of a mixture of suitable amounts depending upon the desired densities of visible and non-visible emitting phosphor is deposited by standard techniques on the inside of the glass faceplate 12 of a cathode ray tube 14. A photo electroluminescent panel 16 is placed on the external surface of the faceplate I2. Panel 16 consists of a first transparent electrode 18, photoconductive material 20, a second transparent electrode 22, electroluminescent material 24 and a third transparent electrode 26.

Referring to FIG. 2 which is a schematic illustration of the invention. A voltage source 28 is applied across electrodes 18 and 26 when switch 30 is moved from contact 32 to contact 34. The total voltage drop across electrodes 10 and 26 is divided between the photoconductive material 20 and the electroluminescent material 24 such that the electric field across the electroluminescent material is below the critical value for the particular material used. When the photon beam from the excited phospphor strikes photoconductive screen 20, its resistance at that point becomes negligible and the total voltage drop appears across electroluminescent screen 24. That spot on 24 will now be illuminated in the long persistence mode. For the short persistence mode switch 30 is moved from contact 34 to contact 32 to provide a short circuit path that insures the discharge of capacitive voltages that may be present.

In practicing the invention the dual phosphors screen 10 may consist of a mixture of approximately 50% phosphor emitting in the ultraviolet, having medium or long persistence and approximately 50% short persistent green phosphor. The relative percentages may be adjusted to provide the desired densities. The photoelectroluminescent panel 16 is transparent to the dual phosphor green emission when the electric field across electrodes 18 and 26 is zero. Electrodes ll, 18, 22, and 26 may be of any of the conventional transparent type. Photoconductive screen 20 may be, for example, cadmium sulfide or try zinc sulfide while electroluminescent screen 24 may be zinc sulfide. When switch 30 is moved to contact 34 and screen 20 is ultraviolet photo excited, the electric field across electroluminescent screen 24 causes it to emit visible radiation (preferably green).

If preferred, panel 16 may be placed on the inside of the faceplate of the cathode ray tube. It being understood that the electrodes must be appropriately placed to provide the necessary electric fields.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A multiple mode cathode ray tube screen for presenting a display of differing persistence comprising:

a. an envelope having a viewing area with a screen supporting surface related thereto;

b. a dual phosphor screen formed on the inside of said supporting surface, said dual phosphor screen being composed of a first phosphor material responsive to optical and cathode ray excitation and exhibiting a phosphorescence of substantially short persistence in the visible spectrum and a second phosphor material responsive to optical and cathode ray excitation and exhibiting a phosphorescence in the non-visible spectrum, said dual phosf. a second transparent electrode layered between said photoconductive material and said electroluminescent material;

g. a third transparent electrode layered on the outside surface of said electroluminescent material whereby a voltage may be established across said first and third electrodes that portion of said electro-luminescent material as said phosphor screen is scanned by the electron beam of said cathode ray tube.

2. The screen of claim 1 wherein said ultraviolet material is cadmium sulfide. 

1. A MULTIPLE MODE CATHODE RAY TUBE SCREEN FOR PRESENTING A DISPLAY OF DIFFERING PERSISTENCE COMPRISING: A. AN ENVELOPE HAVING A VIEWING AREA WITH A SCREEN SUPPORTING SURFACE RELATED THERETO, B. A DUAL PHOSPHOR SCREEN FORMED ON THE INSIDE OF SAID SUPPORTING SURFACE, SAID DUAL PHOSPHOR SCREEN BEING COMPOSED OF A FIRST PHOSPHOR MATERIAL RESPONSIVE TO OPTICAL AND CATHODE RAY EXCITATION AND EXIBITING A PHOSPHORESCENCE OF SUBSTANTIALLY SHORT PERSISTENCE IN THE VISIBLE SPECTRUM AND A SECOND PHOSPHOR MATERIAL RESPONSIVE TO OPTICAL AND CATHODE RAY EXCITATION AND EXHIBITING A PHOSOPHORESCENCE IN THE NON-VISIBLE SPECTRUM, AND DUAL PHOSPHOR MATERIAL BEING APPROXIMATELY 50% PHOSPHOR EMITTING IN THE ULTRAVIOET, HAVING MEDIUM OR LONG PERSISTENCE, AND APPROXAMATELY 50% SHORT PERSISTENCE GREEN PHOSPHOR, AND SAID PHOTOCONDUCIVE MATERIAL BEING ULTRAVIOLET SENSITIVE, C. A PHOTOCONDUCIVE MATERIAL WHOSE RESISTANCE BECOMES NEGLIGIBLE PHOSPHORESCENCE, NON-VISIBLE PHOSPHORESCENCE, D. A FIRST TRANSPARENT ELECTRODE LAYERED BETWEEN THE OUTSIDE SURFACE OF SAID FACE PLATE ANND SAID PHOTOCONDUCIVE MATERIAL, E. AN ELECTROLUMINESCENT MATERIAL RESPONSIVE TO EXCIATION BY THEPRESENCE OF AN ELECTRIC FIELD, F. A SECOND TRANSPARENT ELECTRODE LAYER BETWEEN SAID PHOTOCONODUCIVE MATERIAL AND SAID ELECTROLUMINESCENT MATERIAL, G. A THIRD TRANSPARENT ELECTRODE LAYER ON THE OUTSIDE SRFACE OF SAID ELECTROLUMINESCENT MATERIAL WHEREBY A VOLTAGE MAY BE ESTABLISHED ACROSS SAID FIRST AND THIRD ELECTRODES THAT PORTION OF SAID ELECTRKO-LUMINESCENT MATERIAL AS SAID PHOSPER SCREEN IS SCANNED BY THE ELECTRON BEAM OF SAID CATHODE RAY TUBE.
 2. The screen of claim 1 wherein said ultraviolet material is cadmium sulfide. 